The invention herein relates to free-flowing particulate thermal insulating materials.
The use of siliceous materials for thermal insulation is quite common and many varieties of siliceous insulations are commercially available. In most cases these insulating materials are sold as preformed shapes or as moldable plastic materials. In these forms they are readily attached to most pipes, vessels, etc., which are to be insulated. In some cases, however, the pipe, pipe fitting, or other apparatus which is to be insulated is in an inaccessible position or is of a complex shape. In either case, the system is not amenable to the use of conventional preformed or plastic molded insulations.
In order to overcome these difficulties, pourable or free-flowing insulating materials have been developed. These are commonly particulate, granular, or powdered materials which can be poured dry into the enclosed available space surrounding the system to be insulated. Being free flowing, the granular insulation can be made to completely fill the enclosing space and to conform to the various irregularities in the surface to be insulated.
Such pourable insulations would find use, for instance, for insulating the complex piping in spacecraft and missiles. Inaccessible or compartmented structures such as ship bulkheads or double walls of insulated trucks and railroad cars can also be filled with granular insulation, often at a substantial saving in both construction time and expense over the use of preformed slab insulation. Further, reaction vessels such as those used in chemical plants and petroleum refineries can often be more easily and inexpensively insulated by being surrounded by a simple cylindrical hollow shell filled with granular insulation than by use of block insulations curved to fit the various irregularities of the vessel.
In determining the efficiency of thermal insulation, the thermal conductivity of the insulation in question is generally compared against the thermal conductivity of dry still air at the same temperature. While some insulations have been developed which have thermal conductivities lower than that of dry still air (see, for instance, U.S. Pat. Nos. 2,808,338; 2,811,457 and 3,055,831), most conventional insulations have thermal conductivities two or three times greater than that of dry still air. A thermal insulation that approaches or equals the thermal conductivity of dry still air is therefor considered to be a very superior insulation.